More on roasting:

Feb 12, 2014

The kaleidoscopic array of flavors you find in your coffee from cup to cup is a result of both the natural chemical makeup of the green coffee and the trick we roasters have learned to unlock its potential—we roast it to secret profiles.

The raw coffee bean—not actually a legume but the pit of a small, red fruit—contains roughly 300 volatile compounds, making it chemically well equipped to be turned into a very flavorful beverage. These aromatics, however, are locked away in the bean’s extremely dense cellular structure. Roasting the tiny, rock-hard pits transforms them in two major ways. The first change is to the aromatic compounds. Heating the beans to temperatures of around 400 degrees leads to an increase in kinetic energy—or movement—on the molecular level. As the molecules bump and collide, they rearrange themselves into new formations—some into longer and more complex chains made up of multiple molecules and others into smaller fragments.

Roasted coffee has roughly three times more aromatic compounds than raw beans, which are already relatively rich in them. The bell pepper smell of green raw beans breaks down and recedes while new aromas, perhaps of savory butter or tomato soup, come to the fore. Those varying flavor notes are determined by the raw bean, how and where it’s grown and processed, and how the roaster manages the chemical reactions. Often when a coffee tastes like, say, blueberries, it’s because the very same compounds found in the berry have been formed in the bean.

The other change is to the cellular structure, which becomes porous and brittle when previously almost impenetrably dense. You can imagine the roasted bean as a microscopic honeycomb with tiny pockets of coffee oil instead of honey. The oil contains the bulk of the coffee’s aromatic compounds, and accessing it becomes as simple as breaking open the bean. The consequence, however, is that the volatile compounds begin to oxidize and degrade. While raw coffee can be stored for months without ill effect, the roasted beans are at their peak freshness for only a matter of days, which brings us back to the original question. Remember to imbibe coffee made from fresh beans with their entire array of aromatic compounds—from dried flowers to blueberries to tomato soup—undiminished by oxidation.